In material web forming and handling devices such as paper machines, a boundary layer of air is formed at both sides of the paper web, which usually moves at quite a high speed, as well as at both sides of a textile web or drying wire which is used to carry the paper web. Each boundary layer of air carries along with it dust that has been separated from the fibre mesh of the web and from the fillers in the web. The dust spreads into the environment surrounding the textile machine, paper machine or other device and is partly also carried to the web reel. Moreover, after the manufacture of the paper, dust and contaminants, such as debris and fibers, adhere to the face of the web.
In a paper machine, one important and significant source of dust is the slitting process, in which an abundance of dust is separated from the web when the web is slit into component webs or reels in the longitudinal direction. Problems related to the production and presence of dust also occur in the manufacture of tissue paper, in particular in connection with creping by means of a doctor, wherein the paper web is separated by means of a doctor blade from a face of a steam-heated yankee cylinder, in which connection a particularly large quantity of dust is detached from the web, which dust is drawn along by the paper web and spreads into the surrounding environment. Dust and contaminants cause problems in the further processing of the paper, for example in printing operations, because it is of vital importance from the point of view of the quality of printing that the printing rolls remain clean. Also, dust spreads both in the paper mill and in further processing of the web into the environment, and dust may result in risks for occupational health because it may contain various particles of fillers.
With respect to the prior art, reference is made to the U.S. Pat. No. 3,239,863, which describes a web cleaning device including a chamber space in which two air nozzles have been formed directed at the web. The space between the nozzles is closed so that it forms an exhaust chamber for the air coming out of the nozzles and for the dust separated from the web. In this prior art arrangement, one of the more noticeable problems is how to produce a sufficiently high air blow rate to separate the dust adhering to the web as well as the requirement to construct the device so that it is placed quite far at a distance from the web, in which case it is mainly suitable for general removal of dust, but not for detaching dust or contaminants from the web.
One prior art construction for the problems described above is described in the current assignee's Finnish Patent No. 95,611 (Finnish Patent Application No. 942269) which describes dust removing method and apparatus in which it has been considered novel that the web is subjected to a high-pressure blowing so as to separate the dust from the web and in the running direction of the web, before and after the high-pressure blowing, dust and other particles that has been separated from the web are absorbed.